Which of the following was based on a previous X.500 specification and allows either unencrypted
authentication or encrypted authentication through the use of TLS?

A.
Kerberos

B.
TACACS+

C.
RADIUS

D.
LDAP

Explanation:
The Lightweight Directory Access Protocol is an open, vendor-neutral, industry standard
application protocol for accessing and maintaining distributed directory information services over
an Internet Protocol (IP) network. Directory services play an important role in developing intranet
and Internet applications by allowing the sharing of information about users, systems, networks,
services, and applications throughout the network. As examples, directory services may provide
any organized set of records, often with a hierarchical structure, such as a corporate email
directory. Similarly, a telephone directory is a list of subscribers with an address and a phone
number.
A common usage of LDAP is to provide a “single sign on” where one password for a user is
shared between many services, such as applying a company login code to web pages (so that
staff log in only once to company computers, and then are automatically logged into the company
intranet).
LDAP is based on a simpler subset of the standards contained within the X.500 standard.
Because of this relationship, LDAP is sometimes called X.500-lite.
A client starts an LDAP session by connecting to an LDAP server, called a Directory System
Agent (DSA), by default on TCP and UDP port 389, or on port 636 for LDAPS. Global Catalog is
available by default on ports 3268, and 3269 for LDAPS. The client then sends an operation

request to the server, and the server sends responses in return.
The client may request the following operations:
StartTLS — use the LDAPv3 Transport Layer Security (TLS) extension for a secure connection